Iron golf club

ABSTRACT

The inventive iron golf club comprises a head part having a face, and a restitution coefficient is in the range of at least 0.81 and not more than 0.95 when colliding a ball against a sweet spot in the face at a speed of 44 m/s. In the aforementioned iron golf club, the effective face area of the head part is at least 2500 mm 2  and not more than 5000 mm 2 , the effective deflection length is at least 36 mm and not more than 72 mm, and the thickness of the face is at least 1.0 mm and not more than 2.5 mm at the sweet spot.

[0001] This application claims priority from Japanese patent applicationNo. 2000-145081 (P) filed May 17, 2000 entitled “Iron Golf Club.”

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an iron golf club, and moreparticularly, it relates to an iron golf club capable of improving thecarry by rendering its face readily deflectable at the hit.

[0004] 2. Description of the Prior Art

[0005] U.S. Pat. No. 5,863,261 describes first prior art related to thehead of a golf club. This literature discloses a head part of a golfclub having two face plates fixed to each other with a fluid for causingelastic deformation by a doubler structure and effectively supplying theenergy of the golf club to a ball thereby improving the carry.

[0006] As second prior art, U.S. Pat. No. 5,605,511 discloses a headpart of a golf club having an annular groove provided on the rearperipheral wall part of its face to enclose the central part.

[0007] A golf club is required to get a carry. In particular, a longcarry eases the next shot and influences the score. Repulsiveness of theclubface is remarkably concerned with the carry. Therefore, it isimportant to improve the repulsiveness of the clubface.

[0008] According to the head part of the golf club disclosed in theaforementioned first prior art, it is conceivable to improve therepulsiveness to some extent. However, a great deal of time and laborfor connection and a high cost are required for manufacturing thestructure having two face plates in the first prior art.

[0009] The head part of the golf club according to the second prior art,provided with the annular groove thereby reducing audible vibration, isnot directed the carry of a golf ball. Further, a great deal of time andlabor and a high cost are required for manufacturing the head part dueto the necessity for providing the annular groove.

SUMMARY OF THE INVENTION

[0010] Accordingly, a principal object of the present invention is toprovide an iron golf club having a head part capable of improvingrepulsiveness and increasing the carry of a ball by reducing therigidity of its face without requiring a great deal of time and laborand a high cost for manufacturing the same.

[0011] The iron golf club according to the present invention comprises ahead part having a face, and a restitution coefficient is in the rangeof at least 0.81 and not more than 0.95 when colliding a ball against asweet spot in the face at a speed of 44 m/s.

[0012] Thus, the carry of the ball can be increased not only when theball is hit by the sweet spot but also when hit by a portion close tothe sweet spot due to the high restitution coefficient at the sweet spotof the face. The restitution coefficient can be improved by reducing thethickness of the face, for example, without requiring a great deal oftime and labor or a high cost for manufacturing the iron golf club.

[0013] In the head part of the aforementioned iron golf club, aneffective face area is preferably at least 2500 mm² and not more than5000 mm². Throughout the specification, the term “effective face area”stands for the surface area of a portion of a face part substantiallydeflectable at the hit, such as the surface area of a face centralportion excluding wall potions around the face part in a clubhead havinga hollow structure, for example.

[0014] In the head part of the aforementioned iron golf club, aneffective deflection length is preferably at least 36 mm and not morethan 72 mm. The term “effective deflection length” stands for the lengthof a portion of the face part substantially deflectable at the hit,passing through the sweet spot in a direction perpendicular to theground, such as the length of a portion between wall portions around theface part, passing through the sweet spot in a direction perpendicularto the ground, in a clubhead having a hollow structure, for example.

[0015] In the head part of the iron golf club according to the presentinvention, the thickness of the face is preferably at least 1.0 mm andnot more than 2.5 mm at the sweet spot. Further, the elasticity of theface part is preferably at least 30 GPa and not more than 210 GPa.

[0016] The aforementioned subject matters may be properly combined witheach other.

[0017] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is an exploded perspective view of a head part of an irongolf club according to the present invention;

[0019]FIG. 2 is a sectional view taken along the line 100-100 in FIG. 1,showing a front-part component and a rear-part component assembled witheach other; and

[0020]FIG. 3 shows results of a carry test made on inventive andcomparative samples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In an iron golf club according to the present invention, thethickness of a face in a head part is reduced, for example, therebyimproving a restitution coefficient when colliding a prescribed ballagainst a face part at a prescribed speed. More specifically, therestitution coefficient is set in the range of at least 0.81 and notmore than 0.95 when colliding the ball against a sweet spot at a speedof 44±0.5 m/s in a test method described later.

[0022] When the thickness of the face is reduced as described above, theface part is rendered readily deflectable, i.e., readily elasticallydeformable to be capable of exhibiting a spring effect and improvingrepulsiveness of the face. More specifically, the thickness of the faceis set to at least 1.0 mm and not more than 2.5 mm.

[0023] The term “the thickness of the face” stands for the boardthickness of the face part in a direction perpendicular to the face atthe sweet spot. The elasticity of the face part is preferably at least30 GPa and not more than 210 GPa.

[0024] The repulsiveness of the face can be further improved byincreasing an effective face area, i.e., the area of a deformed regionat the center of the face. More specifically, the effective face area isat least 2500 mm² and not more than 5000 mm².

[0025] In the present invention, the term “effective face area” standsfor the surface area of a portion of the face part substantiallydeflectable at the hit. In an iron golf club having a head part of ahollow structure, for example, the effective face area corresponds tothe area of a face center portion excluding wall portions around theface, such as the area of a portion shown by slant lines in FIG. 1.

[0026] The repulsiveness of the face can be improved by increasing theeffective deflection length, i.e., the length between a sole part and atop edge part at the center of the face. More specifically, theeffective deflection length is at least 36 mm and not more than 72 mm.

[0027] In the present invention, the term “effective deflection length”stands for the length of a portion of the face part substantiallydeflectable at the hit, passing through the sweet spot of the face in adirection perpendicular to the ground. In an iron golf club having ahead part of a hollow structure, for example, the effective deflectionlength corresponds to the length of a portion between wall portionsaround the face, passing through the sweet spot (center of a face scoreline) in a direction perpendicular to the ground. Referring to FIGS. 1and 2, symbol L denotes the effective deflection length.

[0028] In the iron golf club head part having the head part of a hollowstructure, the wall portions around the face conceivably serve assupport portions deforming the face at the hit, and hence the regionenclosed with the wall portions can be readily elastically deformed byincreasing the length between the support portions. Consequently, therepulsiveness is improved as described above.

[0029] Further, the amount of elastic deformation is reduced if thelength between the support portions is small on the portion collidingwith the ball regardless of the effective face area, and hence thelength between the support portions must be increased. Thus, therepulsiveness of the face can be further improved by increasing theaforementioned effective deflection length.

[0030] A method of measuring the restitution coefficient is nowdescribed.

[0031] First, the face of the iron golf club head part is stoodperpendicularly to the ground and the golf ball to be collidedtherewith, and the golf ball is collided against the center of the scoreline of the clubhead or the sweet spot, for measuring the ball speed Vin(Vin=44±0.5 m/s in this method) before collision and the ball speed Voutafter collision with a speed meter having an optical sensor.

[0032] The restitution coefficient COR is calculated from the measuredspeeds Vin and Vout and the following numerical formula (1):

Vout/Vin=(COR×M−m)/(M+m)  (1)

[0033] Where M represents the mass of the head part of the iron golfclub, and m represents the mass of the golf ball. Pinacle Gold LS byAcushinet Company is employed as the golf ball. The golf ball, having anaverage weight of 45.4±0.4 g, is kept in a room maintained at atemperature of 23±1° C. during the test.

[0034] An embodiment of the present invention is now described withreference to FIGS. 1 to 3. FIG. 1 is an exploded perspective view of ahead part 1 of an iron golf club according to the present invention.FIG. 2 is a sectional view taken along the line 100-100 in FIG. 1showing a front-part component 10 and a rear-part component 11 assembledwith each other. Referring to FIGS. 1 and 2, illustration of a shaft anda grip of the iron golf club is omitted.

[0035] As shown in FIG. 1, the head part 1 is formed by integrallyassembling the front-part component 10 and the rear-part component 11with each other. The front-part component 10 has a concave part 13 bprovided on its center, a connection part 6 (wall portion) provided onits peripheral edge, and a hosel 5. The rear-part component 11 has aconcave part 13 a provided on its center and a connection part 6provided on its peripheral edge. The front-part component 10 and therear-part component 11 are integrated with each other by welding theperipheral edges of the connecting parts 6. Welding margins are 2 mm,for example.

[0036] Referring to FIG. 1, the area of the bottom surface of theconcave part 13 b, i.e., the area of the region shown by slant lines,corresponds to the aforementioned effective face area. According to thisembodiment, the effective face area is 2930 mm².

[0037] Further, the length L shown by arrow in FIG. 1 corresponds to theaforementioned effective deflection length, which is 36.5 mm in thisembodiment.

[0038] As shown in FIG. 2, the head part 1 of the iron golf clubaccording to this embodiment is provided in a cavity back structure witha sole part 2 having a larger thickness than a top edge part 3, and hasa hollow structure with a space 12 defined between the front-partcomponent 10 and the rear-part component 11.

[0039] The thickness (face thickness) t of a face part having a face 4serving as a hitting surface is 2.3 mm. This thickness corresponds tothat at a sweet spot.

[0040] The front-part component 10 and the rear-part component 11 areformed by forging stainless steel SUS 630, for example.

[0041] The material for the face is not restricted to the aforementionedstainless steel but may alternatively be prepared from another stainlesssteel such as austenite-based SUS 301, 303, 304, 304N1, 304N2, 305,309S, 310S, 316, 317, 321, 347 or XM7, martensite-based SUS 410, 420,431 or 440, precipitation-hardened SUS 630, ferrite-based SUS 405, 430or 444, soft iron such as S15C, S20C, S25C, S30C or S35C, or specialsteel such as high tension steel, ultrahigh tension steel, ausformingsteel, maraging steel or spring steel. Further alternatively, thematerial can be prepared from a titanium alloy such as pure titanium I,II, III or IV, an α alloy of 5Al-2.5V, an α-β alloy of 3Al-2.5V, 6Al-4V,4.5Al-3V-2Fe-2Mo, a β alloy of 15V-3Cr-3Sn-3Al, 10V-2Fe-3Al,13V-11Cr-3Al, 15Mo-5Zr, 15V-6Cr-4Al, 15Mo-5Zr-3Al, 20V-4Al-1Sn, 22V-4Alor 3Al-8V-6Cr-4Mo-3Zr, an aluminum alloy such as pure aluminum, 2017,2024, 7075, 3003, 5052, 5056, 6151, 6053 or 6061 or a magnesium-basedalloy such as AZ63A, AZ81A, AZ91A, AZ91C, WE54 or EZ33A, while a doublerformed by any combination of these materials is employable.

[0042] The material for the parts other than the face can be preparedfrom a material generally employed for manufacturing a clubhead such asiron, stainless steel, aluminum, titanium, magnesium, tungsten, copper,nickel, zirconium, cobalt, manganese, zinc, silicon, tin, chromium, FRP,synthetic resin, ceramic or rubber, which may be singularly employed.Alternatively, a combination of at least two of these materials may beemployed.

[0043] The face and the remaining parts can be manufactured by precisioncasting, which can be carried out with high dimensional accuracy at alow cost. Alternatively, the head body can be manufactured by diecasting, pressing or forging. Further alternatively, the respectiveparts can be manufactured by pressing, forging, precision casting, metalinjection, die casting, cutting or powder metallurgy and connected witheach other by bonding, press fitting, engaging, pressure connection,screwing, brazing or the like for forming the clubhead.

[0044] Characteristics of inventive sample of the aforementioned headpart and comparative samples A to D of conventional head parts are nowdescribed with reference to Table 1 and FIG. 3.

[0045] Table 1 shows restitution coefficients, sizes and areas of theinventive sample and the comparative samples A to D. Referring to Table1, the comparative sample D, for example, is the so-called cavity backiron clubhead, which is made of soft iron S25C. TABLE 1 Com- Com- Com-Com- Inventive parative parative parative parative No.5 Sample Sample ASample B Sample C Sample D Face Thick- 2.3 3.4 3.2 2.8 3 ness (mm)Effective 2930 2080 1760 2410 1820 Face Area (mm²) Effective 36.5 31.431.9 35.5 29.6 Deflection Length (mm) Restitution 0.815 0.771 0.7850.804 0.784 Coefficient

[0046] Comparing the inventive sample with the aforementionedcomparative sample D in particular, the face thickness is reduced by23%, the effective face area is increased by 61% and the effectivedeflection length is increased by 23%. In the inventive sample, therestitution coefficient of 0.815 is improved by 4% as compared with thatof 0.784 of the comparative sample D.

[0047] Also as compared with the remaining comparative samples A to C,the restitution coefficient of the inventive sample is extremely high asshown in Table 1.

[0048]FIG. 3 shows the carries of the inventive sample and thecomparative sample D. Number five irons with a loft of 26 degrees wereemployed for making a robot test at a head speed of 35 m/s. FIG. 3 showsan average value of six shots as to each sample. As shown in FIG. 3, theinventive sample exhibits a carry of 146.7 m and a total carry of 151.7m inclusive of roll, while the comparative sample exhibits a carry of135.2 m and a total carry of 137.1 m inclusive of roll. Thus, it isunderstood that the carry and the total carry of the inventive sampleare improved by 8.5% and 10.6% respectively as compared with thecomparative sample D.

[0049] According to the present invention, as hereinabove described, therepulsiveness of the clubface can be improved by reducing the rigidityof the face without requiring a great deal of time and labor and a highcost for manufacturing the head part of the iron golf club, forincreasing the carry of the ball.

[0050] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. An iron golf club comprising a head part having aface, wherein a restitution coefficient is in the range of at least 0.81and not more than 0.95 when colliding a ball against a sweet spot insaid face at a speed of 44 m/s.
 2. The iron golf club according to claim1 , wherein an effective face area being the surface area of a portionof said face deflectable at the hit is at least 2500 mm² and not morethan 5000 mm².
 3. The iron golf club according to claim 1 , wherein saidhead part has a hollow structure, wall portions are provided on theperipheral edge of a face part in said head part, and the surface areaof a central portion of said face located between said wall portions isat least 2500 mm² and not more than 5000 mm².
 4. The iron golf clubaccording to claim 1 , wherein an effective deflection length being thelength of a portion of said face deflectable at the hit, passing throughsaid sweet spot of said face in a direction perpendicular to the ground,is at least 36 mm and not more than 72 mm.
 5. The iron golf clubaccording to claim 1 , wherein said head part has a hollow structure,wall portions are provided on the peripheral edge of a face part in saidhead part, and an effective deflection length being the length betweensaid wall portions, passing through said sweet spot of said face in adirection perpendicular to the ground, is at least 36 mm and not morethan 72 mm.
 6. The iron golf club according to claim 1 , wherein thethickness of a face part is at least 1.0 mm and not more than 2.5 mm atsaid sweet spot of said face.
 7. The iron golf club according to claim 1, wherein the elasticity of a face part in said head part is at least 30GPa and not more than 210 GPa.